Recent evidence strongly suggests that nonhistone chromosomal (NHC) proteins regulate the transcription of specific genes. One approach to identifying which NHC proteins are involved in gene regulation is to follow their changes during cytodifferentiation. The changes in NHC proteins of muscle will be investigated during in vitro and in situ myogenesis. NHC proteins will be resolved beyond what has been previously possible by a new technique, involving isoelectric focusing in one direction, followed by discontinuous SDS slab gel electrophoresis in second direction. This will allow the identification of any muscle specific proteins that constitute a relatively minor proportion of the total NHC protein population. Changes in the synthesis, degradation and phosphorylation of both major and minor muscle specific proteins will be compared in rat limb myoblasts, inhibited at specific putative transitions, by growth in media that either promotes a) proliferation, b) contains Bromodeoxyuridine or c) is Ca ions depleted. The interaction of the muscle specific NHC proteins with different parts of the genome will be investigated by comparing the NHC proteins that bind specifically to different fractions of restriction endonuclease digested rat DNA. These studies will contribute to the knowledge of how specific gene transcription is regulated during normal and neoplastic cytodifferentiation.